[#55466076] Split `User` into `ActiveUser` and `PendingUser`.
[#55466076] Add a `create` action to UsersController which creates a pending user.
[#55466076] Add `active` and `pending` scopes to `User`.
[#55466076] Allow only active users to sign in.

- Also rename the `user` factory to `active_user`
- Add a `pending_user` factory.
Add the Fuubar formatter